Ballistic articles such as bulletproof vests, helmets, armor plate, and other military equipment, structural members of helicopters, aircraft, ships, and vehicle panels and briefcases containing high strength fibers are known. Fibers conventionally used include aramid fibers, fibers such as poly(phenylenediamine terephthalamide), graphite fibers, ceramic fibers, nylon fibers, glass fibers and the like. For these applications, the fibers are ordinarily encapsulated or embedded in a rigid matrix material and, in some instances, are joined with rigid facing layers to form complex composite structures.
U.S. Pat. No. 4,403,012 and U.S. Pat. No. 4,457,985 disclose ballistic-resistant composite articles comprised of networks of ultra-high molecular weight polyethylene or polypropylene fibers in matrices composed of olefin polymers and copolymers, unsaturated polyester resins, epoxy resins, and other resins curable below the melting point of the fiber. While such composites provide effective ballistic resistance, A. L. Lastnik, et al.; "The Effect of Resin Concentration and Laminating Pressures on KEVLAR.RTM. Fabric Bonded with Modified Phenolic Resin", Technical Report NATICK/TR84/030, June 8, 1984, has disclosed that an interstitial resin, which encapsulates and bonds the fibers of a fabric, reduces the ballistic resistance of the resultant composite article. Therefore, a need exists to improve the structure of composites to effectively utilize the properties of the high strength fibers.
U.S. Pat. application Ser. No. 691,048, Harpell et al., filed Jan., 14, 1985, and commonly assigned, discloses a simple composite comprising high strength fibers embedded in an elastomeric matrix. Surprisingly, the simple composite structure exhibits outstanding ballistic protection as compared to sample composites utilizing rigid matrices, the results of which are disclosed therein. Particularly effective are simple composites employing ultra-high molecular weight polyethylene and polypropylene such as disclosed in U.S. Ser. No. 4,413,110. However, the simple composites, because of the use of a low modulus elastomeric matrix, may not be suitable in some applications where, for example, rigidity, surface hardness, chemical resistance or heat resistance may be very important.
We have discovered complex composite structures which do not compromise the advantageous properties of a simple composite formed of fibers in a low modulus elastomeric matrix while providing the requisite rigidity, surface hardness, chemical resistance or heat resistance, etc., needed for certain applications. Moreover, complex composite structures of this invention are unexpectedly superior to the simple composite in ballistic protection (at equal weight).